>> this program is found in
4.7.3 and the lesson is pointer constants and
>> pointer  constants expressions.
>
> Ah! Apparently the chapters are numbered differently in the Linux
> version, too...
>
>
1.7.3 Pointer Constants and Pointer Constant Expressions
>
> HLA allows two literal pointer constant forms: the address-of operator
> followed by the name of a static variable or the constant zero. In
> addition to these two literal pointer constants, HLA also supports
> simple pointer constant expressions.
>
> The constant zero represents the NULL or NIL pointer, that is, an
> illegal address that does not exist. ...
